The present invention relates to electrodes used in the transfer of radio frequency energy to a substance and more particularly to electrodes used in the medical treatment of living tissue in animals by hyperthermia techniques.
It has been well known for sometime that many substances, including animal tissue, respond by heating to the passing of radio frequency (RF) energy therethrough. In particular, this has found application in the selective destruction of certain tissues within living animals including humans. More specifically, it has been found that because tumors (both malignant and benign) have a reduced capacity for the passage of blood therethrough with attendant cooling thereby, the application of RF energy to the tumor and the surrounding tissue will cause the tumor to be elevated to a higher temperature than the surrounding tissue. It is possible, by careful control of the RF energy applied, to raise the temperature of the tumor above the point were necrosis of the tumor will occur while maintaining the temperature of the healthy surrounding tissue below the destructive temperature level. By such a technique, the tumor is destroyed while the surrounding healthy tissue is undamaged.
It has been common practice in the prior art employing such techniques to connect a pair of paddle type electrodes to a source of RF energy. The electrodes are then disposed on either side of the tissue containing the tumor in the manner shown in FIG. 1. The RF energy passes between the electrodes 10 with the tissue containing the tumor behaving in a manner of a dielectric in a capacitor. Ordinarily, the tissue placed between the electrodes is a complex substance with varying resistances such that those components with the greatest resistance (e.g. skin 12 and subcutaneous tissue 14) are preferentially heated, while those components with lower resistance and those more deeply located (e.g. muscle 16 and the tumor 18) are least heated. In practice, this generally results in the inability to heat deeply, or in superficial heat absorption which results in burning. Since tumors and various disease states potentially treatable by heat are often located deep within the body, a method and apparatus for allowing deep heating without skin and subcutaneous tissue injury would be desirable. To date, with the apparatus of the prior art, the only method for treatment of deeply located tissues by hyperthermia was through the surgical implantation of the electrodes. That is, the tissue to be treated is surgically exposed so that the paddle type electrodes can be disposed on either side and close adjacent to the area of treatment.
A spiral, pancake type coil has also been used commercially. It produces a localized magnetic field which attenuates very rapidly with spacing from the body. It also has a large voltage build-up between turns thus creating a related voltage gradient across the skin surface in that region. The result is superficial heating in the skin and subcutaneous fat layer. Such an electrode is, therefore, of little value in deep medical treatment by hyperthermia.
Wherefore, it is the object of the present invention to provide an electrode for use in medical treatment by hyperthermia which allows deep heating by the transfer of radio frequency energy without the attendant hazards to healthy tissues described above.